The Hydroelasticity Analysis Of Ship Wave Loads And Its Effect On Fatigue Strength

With the development of the marine industry, ships are increasingly shifting into large-scale and specialization. Large-scale vessels always have the feature of a large slenderness ratio, resulting in its stiffness being much lower compared with the conventional vessels. For that reason this kind of ships are easily affected by waves generating springing to increase the ship hull elastic deformation and give rise to a very bad effect on the fatigue. The traditional method with the assumption of the 2-D planar flow, rigid body model without including the effect of elastic deformation of hull and the linear potential flow theory only suitable for low sea state and low forward speed gradually expresses its limitation. Based on 3-D linear hydroelasticity theory, the section loads of ship can be obtained in this paper. Besides, the model test is designed to verify the rationality of theoretical calculation results. In addition, the springing's influence on the ship fatigue strength was discussed. The main contents of this paper are as follows:(1) Ship is simplified as a ship hull girder, and is divided into 20 parts. Every part would be a Timoshenko beam. In the paper, Transfer matrix method is used for symmetry dry modal analysis of the vertical of the girder. Then, a high-speed vessel is taken as an example to figure out the curve that shows the variation of ship's structural characteristics with the length of the ship and also the natural variation modes in each order are calculated.(2) In order to verify the hydroelasticity theroy's the numerical results and truly reflect ship's elasticity effect, a high-speed vessel model is designed based on the principles that the first order natural frequency of model should be similar to the real ship, and that geometric similarity, movement similarity and gravity similarity.(3) Based on 3-D linear potential flow theory, taking into account the elastic deformation of structure, the three-dimensional hrdyoelasticity method of linear frequency domain is analyzed and researched. Choose a high-speed vessel to verify the method by comparing the results between the numerical results and experimental results. Moreover, though this example, the elastic effect of wave load is discussed.(4) Spectral analysis method of fatigue life assessment process is introduced breifly. Take the example of an ore carrier to compare the calculated fatigue life between rigid theory method and 3-D linear hrdroelasticity theory. By contrast, the influence of elastic effect for fatigue strength is discussed.